This invention relates generally to aviation crash sensors and, more particularly, to a crash sensor which senses acceleration along three orthogonal axes and processes acceleration vector data to detect an omnidirectional crash.
Mechanical acceleration threshold detection devices have been used in the automotive industry to lock seat belt retractors to restrain occupants in their seats in the event of a sensed threshold acceleration along the vehicle longitudinal axis to indicate a frontal crash. These devices are normally mechanical devices utilizing a pendulum or a ball-and-ramp arrangement to sense acceleration in one or two planes. Recently, TRW has developed a seat belt tensioning retractor for Mercedes-Benz that is activated by the automobile on-board computer when it senses a 0.7 G frontal impact to pretension the passenger seat belts.
With the advent of air bags, electronic accelerometers have been devised to actuate air bags. Such electronic accelerometers are illustrated in U.S. Pat. No. 3,762,495--Usui et al and U.S. Pat. No. 4,984,464--Thomas et al. However, none of these automotive crash sensing devices or systems is useful for detecting crashes which do not occur in the horizontal plane of vehicle operation, such as rollover crashes.
Mechanical accelerometers have also been used in the aircraft industry to activate a safety device, such as to lock an aircraft occupant's shoulder harness retractor or to tighten the harness when a threshold acceleration is sensed. A crash sensor for an airplane was previously developed to cut out the electrical circuit, cut off fuel and operate fire extinguishers when a crash was detected, as shown in U.S. Pat. No. 2,573,335. However, these accelerometers are mechanical and react relatively slowly to a crash, thus slowing activation of the safety devices.
An impact indicator was previously developed to detect when aircraft landing gear has been stressed beyond predetermined critical limits. U.S. Pat. No. 3,389,607--Kishel discloses such a system, which utilizes a complex mechanical triaxial acceleration sensor.
Many aircraft crashes or impacts are not necessarily catastrophic, in that they could be survivable by the aircrew if movement of the aircraft occupants during the crash is restrained. For example, helicopters may suffer engine or rotor failures as a result of combat damage or other malfunctions, which will cause a relatively low-speed crash. These crashes could be survivable by the aircrew if the aircraft crewmen were quickly secured in their seats in a manner to limit their so-called "flail envelope".
It would be desirable to provide a crash sensor having three-axis sensing which compares aircraft accelerations to a crash algorithm for each of a variety of different aircraft.
It would also be desirable to provide a crash sensor which automatically identifies the aircraft mounting orientation and automatically converts sensed accelerations into vehicle axis equivalents.
It would further be desirable to provide a method of and apparatus for evaluating vehicle acceleration data for a plurality of different vehicles having axes which are different from the measurement axes to identify a predetermined event.